<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="root"></div>
</body>
</html>
<script src="https://unpkg.com/vue@next"></script>
<script>
    const app = Vue.createApp({
        data(){
            return{
                count:'a',
            }
        },
        methods:{
            handleAdd(count){
                this.count += count;
            }
        },
        template:`
        <div>
            <counter v-model.uppercase="count" />
        </div>
        `
    });
    app.component('counter',{
        props:{
            "modelValue":String,
            "modelModifiers":{
                default:()=>({})
            }
        },
        methods:{
            handleClick(){
                let newValue = this.modelValue+'b';
                if(this.modelModifiers.uppercase){
                    newValue=newValue.toUpperCase();
                }
                this.$emit('update:modelValue',newValue);
            }
        },
        template:`
        <div @click="handleClick">{{modelValue}}</div>
        `
    })
    const vm = app.mount('#root')
</script>